x-ray apparatus



May 9, 1950 J. M. LEDEBOER ET AL.

X-RAY APPARATUS Filed April 25, 1946 JOHANMLARIE 150520.522 Azvrojvzw mmzzMzlsmvam/wm INVENTORS.

BY Wm .A WW4 ATTOIZNZYJ i atented May 9,

J chant ram Lec'l ehder Vingerhoets; Eifn'dhov en, Netherlands: assignors;

by iinesnejassignfnents, to Hartford National Bank andTrust'CoinpanyjHartford; -Conm, as

trustee A pli udnjalirn'. 25, 1946., S erialNo.1664i728 In the Netherlands N o ember 10, 1942 Section 1-,- Pj1blic new 690; August 8, 1946 Patent expires-November 10, 1962 5 claims. 01. 250 95) It' isisgenerally desirable tha't if the voltage 'of an-X ray tubeis altered thestrength of the'current passing through'the tube should also be altered sothat'the load of the tube is maintained at a favourable value.

"Itis known toj-couple the-member for the'com tr'el of the' 'current=with'that for the control of th'eh tube voltage so' that the -current-strength is' -automat-ic'ally controlled by means or the voltby -ineans =o-f a voltage-selector which also con trols'= the voltage of the primary of am auxiliary tra nsforiner whose secondary is included in-the cathode heating circuit of the X-ray tube. the

:arr'angement'being such'that anincrease of the tubevoltage results in 'adecrease of the filament heating current and thus of the current pass- :ing through' theX ray' tube: Thus, it can-be ensured that the tube is "always loaded 'subs'tan- Y 'tiall'y with the '==maximun1 current strength that .is' admissible' at the adjusted tube voltage.

The admissible maximum capacity of the tube 1 debends enythe loading period. With a shorter iloading 'peri'od "a higher tube currentis admissibletlian 'with "a longer loading ='period. For this. :reason X ray apparatus have been constructed: :in which -the' stren'gth of. the tube =currentis .not "dependent-upon-theadjusted-tube voltage" butane on the' loading-period. In this-case the control members of the tube "current, the tube volta' 'ge "'and 'the loading period are jsocoupledxtog ether lthat' the '-'X-ray tube is -continuously' lloade'd'with the=maximum'adinisslble power. Such fX-fra y apparatus are used in X-ray diagnosis} iload-ing the X-ray tube with a power the tubeius't *capabl'e offstandi'rigat the adjusted '1oad iiilg periodensures the advantage that the time necessary for taking photographic exposures, for

exampleiof'moving partsof the human body, can- Such X-r'ayapparatus may-abeused-fwith' advantage for example for testingsmoving machine' parts. Due to the tube be as short as-possible.

cu-rrent being automatically.controlled in accordance with the tube voltageiand'the loading period the preparatory time' for taking exposures is also shorter and. the probability. of errors being committed leading to a failure of the exposures islv'ery slight. 7 V H I If the .tube voltage is to-be kept constant continuously the strength of the tube currentmay also be caused to depend solely on the loading period. 1

y In these known X- -ray apparatus it has always been necessary gto allow a certain play between the power automatically adjusted by the appa- 2 ratus'and the limit of the really admissible ca pacity of the X ray tube. According to the in'- vention it has been found age and/or loading period accidental load variations'inay' occur. A few causes'responsible to thisrnay be indicated such'as the generallyin evita'ble ivar-iations'of the supply voltage and the variations thatma'y'occur in-the emissive powerof the'incandescent'cath'ode' of the X-ray tube.

The invehti'on"has=for its object to' obviate theisaid disadvantages of X-ray apparatus i'n which the'mmber-for controlling the tubeicur rent is coupled to the-members for controlling the tube voltage and/or load duration and to inorease the load capacity of the X-ray tube.

Accordingto theinvention, the apparatus comprises a device for maintaining'the tube currentsubstantially constant at the value adjusted by the said co-ntrol members. Preferably, the member that controls-the tube current in accordance With the tubevoltage and/or the loading period is united with a device for keeping constant the tube current (withi'tube voltage and/or loading period originally adjusted) to 'form a single con tro l device.-

Thecontrol de'vice' may advantageously be formed by: a variable impedance-which isineluded in the heating circuit of the X--ray tube.

and whose valueus dependent upon the adjustment of current and/or the loading period as Well as on the'current passing through the X-ray tube. :The control device may be formed-by a choke coil having direct current pre-magnetisation. Thischoke coil may comprise a closed core having three columns By arranging two windings'on the two external 'limb s'and including them'in heating circuit provision' it can be ensuredthe that alternating current magnetis'ation does not occur in the centralcolumn. This column has arranged. on it one orm'ore Icontrol windings and the current passing throug'h these windings is rendered dependent on the members for the'control of the tube voltage and/or the loading period; inaddition, the central column is provided with a windingw /hich has passed through it 'ai'current whose magnitude is governed by the current passing through the X-ray tube.-

In the apparatus according to the invention the value of the tube'currentis not onlya'utomatic'allyfcontrolled in accordance with the tube voltage and/or the load durationbut with 'a given adjustment of the members 'for the control of the 7 that in spite'of the automatic couplingo-f the control membersof' the current strength'with those of the tube voltthe nieinbers'for controlling the tube tube voltage and/or the loading period the tube current is also automatically kept substantially constant so that accidental variations of the supply voltage or the emissive power of the incandescent cathode of the X-ray tube do not exercise any influence or only exercise a slight influence on the tube current and thus on the load of the X-ray tube. The invention permits of the value of the automatically adjusted capacity of the X- ray tube being chosen to be closer to the limit of the still admissible capacity than it used to be.

X-ray apparatus are known in which measures are taken to keep the strength of the discharge current passing through the X-ray tube substantially constant during the time of operation, the heating current being cut down at an increasing tube current. These measures are, however, not taken with X-ray apparatus in which the control of the tube current is efiected by the members for controlling the tube voltage and/or loading period.

In order that the invention may be clearly understood and readily carried into effect it will now be described more fully with reference to the accompanying drawing, in which by way of example Figures 1 and 2 show the circuit diagrams of two embodiments of the invention.

The X-ray tube l, which comprises an anode 2 and an incandescent cathode 3, is connected with the interposition of a rectifier valve 4 to a terminal of the secondary 5 of a high-voltage transformer 6. The incandescent cathode 3, which is supplied from the heating current transformer 1, is connected to earth at 8. The discharge current passes through a milliammeter 9 and then through a resistance It which has one end connected to the other terminal of the transformer winding 5 and to a terminal of the condenser H. The other terminal of the condenser is connected to the anode of the X-ray tube. When the X-ray tube is in use it has passing through it pulsating direct current which is smoothed by the condenser. This current sets up a potential difference between the ends of the rheostat It.

The primary [2 of the high-voltage transformer 6 is connected with the interposition of a voltage selector 13 to an autotransformer M which iorpart of its winding receives the voltage via connecting terminals I5-lfi for the supply voltage. By means of the voltage selector 13 the primary voltage of the high-voltage transformer is controlled while at the same time the winding 11 which is arranged on the central column of a choke coil i8 is connected with the interposition of a rectifier 29 to the voltage selector !3. The two outer limbs of the core have arranged on them a winding which is formed by two parts l9-20 and is connected in series with the primay of the heating-current transformer l. The operation of the choke coil relies on influencing the permeability of the iron core through the direct current pre-rnagnetisation. The higher the direct current that sets up the pre-magnetisation, the smaller is the permeability so that the inductive resistance of the alternating current winding l929 decreases. The pre-magnetisation is due to the current in the winding 2| which is supplied by the battery 22. The control of the current strength passingthrough the X-ray tube is automatically effected with the aid of the voltage selector |3 by means of which the voltage at the winding F on the choke coil is adjusted. The connection must be such that if higher operating voltages for the X-ray tube are chosen the current in the winding l'l sets up a magnetic field which is oppositely directed to the field of the winding 2! so that an increase of the current strength results in a decrease of the direct current pre-magnetisation of the choke coil. Due to this the inductive resistance of the alternating current winding increases so that the heating current of the tube decreases. Connecting the voltage selector to the lower tube voltages has the opposite efiect and increases the current passing through the X-ray tube. The source of voltage 22 has part of the resistance Hi connected in series with it. The potential difference at the resistance It) brought about by the discharge current passing through the X-ray tube is oppositely directed to the voltage brought about by the battery current so that an increase of the current passing in the tube results in a decrease of the direct current that passes through the magnetisation winding 2!. This decrease in current results in a reduction of the pre-magnetisation so that the inductivity of the choke coil increases and thus the resistance of the alternating current winding. This results in a decrease of the heating current of the X-ray tube so that the current in the X-ray tube is also reduced. This has the efiect of the tube current being automatically stabilised at a value capable of being adjusted by means of the movable contact 23 on the resistance l0 and which is so chosen in connection with the load characteristic curve of the X-ray tube used that at a given voltage at the tube the optimum current strength occurs. A different adjustment of this contact will generally be required on the tube being replaced-with another.

Referring to Figure 2, the core of the choke coil is shown to be provided with a number of windings. The pre-magnetisation of the core is effected by means of a separate winding 23 which is connected to the terminals 24-45 of a source of direct current. A variable resistance 26 connected in series with the winding serves for the adjustment of the current strength in the tube in accordance with the Value corresponding, according to the nomogram, to a given voltage. The pre-magnetisation is influenced by the current in the winding I! which is obtained through a rectifying device 29 from part of the winding of the series-connected transformer it and is adjusted by the voltage selector l3 simultaneously with the tube voltage. This device permits of the X-ray tube being constantly quite automatically operated with the full load. For this purpose the control choke coil has arranged on it a further winding 30 having passing through it direct current which is adjusted as a function of the loading period. For this purpose a time-switch device is shown to comprise a three-electrode valve 3| Whose grid is connected to an R. C.-circuit 32-43. The adjustment of the time period is effected by the choice of the cathode potential by means of a potentiometer 34 which is connected to a source of direct voltage 35 in parallel with the R. C.-circuit. Simultaneously with the adjustment of the cathode voltage the current in the winding 30 is also controlled. The X-ray tube and the devices associated therewith by means of which the voltage supplied by the transformer 6 is rectified are not shown in the drawing. The winding 5 has passing through it alternating current which is proportional to the current passing through the X-ray tube. By obtaining current from the resistance 21 which upon rectification by the system 28 passes through the winding 2| on the iron core 18 of the choke coil the direct current premagnetisation varies in accordance with the tube current variations.

By a proper choice of the various currents the direct current pre-magnetisation can be influenced in such sense that at any adjustment of the control members the tube is loaded to the limit of its capacity and the tube current remains constant with this adjustment irrespective of other influences.

What we claim is:

l. A control circuit for an X-ray tube comprising a low tension circuit for energising the cathode of the tube including an iron core variable reactor for controlling the energisation of the oathode, a separate high tension circuit for applying a potential to the anode of the tube including means to select a potential of desired value and means to derive a unidirectional potential proportional to the selected potential, means to derive a potential proportional to the current flowing through the tube, and means to premagnetize the core of said reactor, said variable reactor comprising a first winding coupled to said means for deriving a unidirectional potential proportional to the applied potential for varying the reactance thereof in accordance with the applied potential and a second winding connected to the means for deriving a potential proportional to the current flowing through the tube for varying the reactance thereof in accordance with the current flowing through the tube.

2. A control circuit for an X-ray tube comprising a low tension circuit for energising the cathode of the tube including an iron core variable reactor for controlling the energisation of the cathode, a separate high tension circuit for applying a potential to the anode of the tube including means to select a potential of desired value and means to derive a unidirectional potential proportional to the selected potential, means to derive a unidirectional potential proportional to the current flowing through the tube, and means to premagnetize the core of said reactor, said variable reactor comprising a first winding coupled to said means for deriving a unidirectional potential proportional to the applied potential for varying the reactance thereof in accordance with the applied potential and a second winding magnetically opposed to the first winding and connected to the means for deriving a potential proportional to the current flowing through the tube for varying the reactance thereof in accordance with the current flowing through the tube.

3. A control circuit for an X-ray tube comprising a low tension circuit for energising the cathode of the tube including an iron core variable reactor for controlling the energisation of the cathode, a separate high tension circuit for applying a potential to the anode of the tube including means to select a potential of desired value and means to derive a unidirectional potential proportional to the selected potential, means to derive a unidirectional potential proportional to the current flowing through the tube, means to derive a unidirectional potential proportional to the loading time of the tube, and means to premagnetize the core of said reactor, said variable reactor comprising a first winding coupled to said means for deriving a unidirectional potential proportional to the applied potential for varying the reactance thereof in accordance with the applied potential, a second winding connected to the means for deriving a potential proportional to the current flowing through the tube for varying the reactance thereof in accordance with the current flowing through the tube, and a third winding connected to the means for deriving a potential proportional to the loading time of the tube for varying the reactance thereof in accordance with the loading time.

4. A control circuit for an X-ray tube comprising a low tension circuit for energising the cathode of the tube including an iron core variable reactor for controlling the energisation of the cathode, a separate high tension circuit for applying a potential to the anode of the tube including means to select a potential of desired value and means to derive a unidirectional potential proportional to the selected potential, and means to derive a unidirectional potential proportional to the current flowing through the tube including a source of direct current potential for premagnetizing the core of said reactor, said variable reactor comprising a first winding coupled to said means for deriving a unidirectional potential proportional to the applied potential for varying the reactance thereof in accordance with the applied potential, and a second winding magnetically opposed to the first winding and connected to the means for deriving a potential proportional to the current flowing through the tube for varying the reactance thereof in accordance with the current flowing through the tube.

5. A control circuit for an X-ray tube comprising a low tension circuit for energising the cathode of the tube including an iron core variable reactor for controlling the energisation of the cathode, a separate high tension circuit for applying a potential to the anode of the tube including means to select a potential of desired value and means to derive a unidirectional potention proportional to the selected potential, means to derive a unidirectional potential proportional to the current flowing through the tube, means to derive a unidirectional potential proportional to the adjusted loading time of the tube, and means to premagnetize the core of said reactor, said variable reactor comprising a first winding coupled to said means for deriving a unidirectional potential proportional to the applied potential for varying the reactance thereof in accordance with the applied potential, a sec ond winding connected to the means for deriving a potential proportional to the current flowing through the tube for varying the reactance thereof in accordance with the current flowing through the tube, and a third winding connected to the means to derive a unidirectional potential proportional to the loading time for varying the reactance thereof in accordance with the loading time, said first, second and third windings being disposed on the central leg of a shell-type core of the reactor.

JOHAN MARIE LEDEBOER.

ANTONIUS WILHELMUS VINGERHOETS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,999,736 Morrison Apr. 30, 1935 2,319,378 Weisglass May 18, 1943 2,404,905 Garretson July 30, 1946 

